They responded in the rear of the K-4 Fanny M. Hillers School off Longview Avenue, which was closed for summer vacation, around 8:30 a.m.
Members of Engine 2 quickly extinguished the smoky fire, which was contained to the engine compartment.
No injuries were reported.
The cause wasn't immediately known.
VIDEO: HACKENSACK FIRE DEPT.
Click here to follow Daily Voice Mahwah-Ramsey and receive free news updates.